SYDNEY (Reuters) - Black Portuguese millipedes are suspects in a rear-end collision between two trains in Western Australia on Tuesday after hundreds of the tiny creatures were found squashed in a slippery mess on the track.

“Millipedes are one of the factors we are going to take into account,” David Hynes, spokesman at the Public Transport Authority of Western Australia, told Reuters.

Six passengers were treated for stiff necks after a train pulling into a station at Clarkson, 40 km (25 miles) north of Perth, ran into a stationary one, the train company said.

“What happened in previous instances is trains which were travelling at speed have gone over an infestation, crushed them and made the tracks slimy. The train loses traction and the train has slipped,” Hynes said.

The millipedes are attracted to moist environments and are seen as invasive pests at high population levels. In 2009, thousands of them overran 2 km (1.2 miles) of track, causing train delays and cancellations near Melbourne in southeast Australia.